The invention relates to a device for reducing the power consumption of a conventional fluorescent lighting installation of the type having one or more but generally two fluorescent lamps operated from a high power factor conventional ballast connected to a conventional electrical power source.
Fluorescent lamp fixtures are extensively used in domestic, business and industrial installations. Installations employing such lamps usually consist of fixtures with two lamps controlled by an encapsulated ballast which starts the lamps and maintains individual lamp filament voltages and currents as specified by the fixture manufacturer. A typical ballast and two lamp fixture has lamp filament, or cathode, voltages of 3.1 to 3.8 volts at a current of 0.750-1.2 amperes. The voltages across the lamps after warm up are 98-102 volts with a current of approximately 0.4 ampere. The power consumption of such lighting installations is significant, and because of their extensive coverage and prolonged use, various methods and devices have been employed to reduce the cost by limiting the power consumed by the lamps.
A procedural method to reduce lighting costs is to remove some of the lamps from the installation fixtures and replace them with non-illuminating, but conducting tubes as disclosed in the patent to Burgess, U.S. Pat. No. 4,255,692. This procedure is generally undesirable since the illumination provided by the fixtures is greatly reduced.
An alternate approach employed to reduce lamp fixture power consumption is to add an impedence device to the fixture circuitry which is connected in series between the ballast and a lamp filament to reduce the operating current flow through the lamps. This approach has been adopted due to the difficulty of changing internal components of the standard ballast resulting from the encapsulation of the ballast. Such devices consist essentially of a standard step-up isolation transformer and a capacitor connected in the circuit between an input lead of the transformer primary and a corresponding output lead of the transformer secondary. The capacitor functions to provide increased capacitive reactance in the series circuit consisting of the ballast and lamp filaments, thus reducing the alternating current flow when the lamps are conductive. The device disclosed in U.S. Pat. No. 3,954,316 to Luchetta is representative of such a current limiting device. Although the foregoing design does achieve lamp current flow reduction in the lighting fixture, significant problems are encountered by its use. As previously mentioned, the voltage and current characteristics for the lamp filament circuits are established by the fixture and ballast manufacturer to produce optimum lighting performance. In a fixture without a power reducing device, the lamp voltages and current are designed to be of specified values and approximately equal at each lamp. The circuit parameters are altered by the addition in the fixture circuitry of a current limiting device which presents an impedence mismatch or unbalanced load created by the prior art capacitor transformer circuit of the device. In addition, the degree of unbalance is different depending upon the random connection of the device in the fixture circuitry, that is which transformer primary lead is connected to which ballast filament output lead in making the installation of the device in the lamp fixture. The variation in lamp filament voltage can be as great as 0.4 of a volt as a result of an improper connection resulting in consequent lower lamp filament voltage. Low filament voltage results in poor operating conditions, non starting, or shortened lamp life. This unbalanced voltage condition results when a random wrong choice is made in connecting the step-up isolation transformer primary leads. Thus, without great care and/or additional effort in installation, the current limiting device may be installed so as to reduce significantly lamp fixture performance.
The patent to Abernathy, U.S. Pat. No. 4,135,115, seeks to correct the intrinsic impedence mismatch possibility of the available current limiting devices by employing two capacitors connected respectively in circuit across each transformer primary input lead and secondary output lead in an effort to establish a symmetrical load. However, the provision of two capacitors adds to the size, complexity, and cost of the device.
It is desirable therefore to provide a power reduction device for use with fluorescent lamp fixtures that inherently provides for a more balanced and symmetrical electrical impedence in limiting lamp fixture current. Applicant's invention achieves this result.